You can use each ticket presale code for one transaction, one show, one seat type.
So you can buy 4 P1 tickets for Sydney, or 4 GA for Sydney. Not 2 P1 and 2 GA for Sydney. You also can't buy 2 P1 for Sydney and 2 GA for Melbourne.
All ticket selections must be the same venue and same ticket location.
If you only bought 2 tickets in the previous presale, you can't use them again, as that is mixing up the ticket selection.
So you can buy 4 P1 tickets for Sydney, or 4 GA for Sydney. Not 2 P1 and 2 GA for Sydney. You also can't buy 2 P1 for Sydney and 2 GA for Melbourne.
All ticket selections must be the same venue and same ticket location.
If you only bought 2 tickets in the previous presale, you can't use them again, as that is mixing up the ticket selection.